A cholesteric liquid crystal (ChLC) material consists of a nematic liquid crystal and a chiral additive blended together to spontaneously form a helical structure with a well defined pitch. This pitch determines the wavelength of light reflected by the material and hence the color of it. The color can also be adjusted by varying the ratio of the nematic liquid crystal and chiral components. A pixel in a ChLC display can be switched between its planar reflective (colored) state and its semi-transparent focal conic state by application of an appropriate drive scheme.
FIG. 1 illustrates a single color ChLC display 10, including a stack having the following layers in the configuration as shown: a substrate 12; an electrode 14; a ChLC material 16; an electrode 18; a substrate 20; and a black absorber 22. A reflection 26 from ChLC material 16 results in a displayed color. A full color ChLC display can be constructed by stacking a set of RGB panels with the individual RGB subpixels overlapped on top of each other and reflecting different regions of the spectrum. The back of the display panel is coated with broadband absorber 22 that absorbs the light not reflected by the preceding layers. Black absorbers include the following exemplary materials: KRYLON matte or glossy black acrylic enamel spray paint.
FIG. 2 illustrates a prior art electrode 30 for a ChLC display. A substrate 38 provides support for the device. The prior art electrode includes two layers of transparent conductive oxide (TCO) layers 32 and 36 separated by a continuous layer of dielectric polymer 34.
Interfacial reflections 24 and 28, shown in FIG. 1, can occur between the layers, for example at the interfaces of the substrates and electrodes, and such interfacial reflections are undesirable in that they degrade device performance. Reflection losses in other types of reflective and emissive displays can also be detrimental to their performance. Furthermore, for flexible displays and solid state lighting devices, the brittleness of standard TCOs, such as indium tin oxide (ITO), can lead to premature device failure due to cracking and loss of conductivity of the TCO.